This invention relates generally to a digital communications receiver, and more specifically, to a method and apparatus for reducing the required dynamic range of the digital communications receiver.
Wireless communication systems have grown tremendously in popularity and are a widely used link in today""s modem communications systems. In general, wireless communications systems comprise a base unit and one or more mobile units serviced by the base unit. Each of the mobile and/or base units comprise a receiver and a transmitter. The information that is exchanged via these base and mobile units may include, for example, voice or data information. One example of a wireless communications system is a cordless telephone system which can be found in many homes and businesses. Another is a cellular phone system.
One problem that currently exists in wireless communications systems is the variation in received signal power resulting from variations or changes in distance between receivers and transmitters in the system. For example, in a wireless communications system comprising a cordless telephone and an associated base unit, the power of the signal received by the cordless phone (mobile unit) is significantly greater when the phone is proximate the base unit than it is when the phone is remote from the base unit. In many cases, this variation in received signal power may be of the same order of magnitude as the variation in signal power due to fading, i.e., 60 dB.
This variation in received signal power translates into a wider dynamic range requirement of receivers employed in the system. For example, in a wireless communications system in which the variation in power due to fading is about 60 dB, and that due to variations in distance between the transmitter and receiver is about 40 dB, the required dynamic range of the receiver is about 100 dB. The increase in the required dynamic range due to distance variations is about 40 dB.
This increase in the required dynamic range of the receiver translates into a receiver which is more complex and expensive, and consumes more power and space than a receiver not subject to this requirement. The problem is particularly acute for digital receivers in which an analog-to-digital (A/D) converter is employed to convert the received signal into a digital format. The increase in the dynamic range requirement directly translates into increased cost, space, and power consumption of the A/D converter. However, for many markets, such as the consumer market, the increase in cost, space, and power consumption which results makes it infeasible to use a digital receiver in the wireless communications system. Although these increases can be offset somewhat by reducing the resolution of the A/D converter, e.g., from 16 to 8 bits, in many cases this results in unacceptable deterioration of signal quality.
Accordingly, an object of the subject invention is a method and apparatus for reducing the required dynamic range of a digital communications receiver configured for use in a wireless communications system without significant deterioration in signal quality.
Another object is a method and apparatus which overcomes the disadvantages of the prior art.
Further objects include utilization or achievement of the foregoing objects alone or in combination.
Additional objects and advantages are set forth in the description which follows or will be apparent to those of ordinary skill in the art who practice the invention.
To achieve the foregoing objects, and in accordance with the purpose of the invention as broadly described herein, there is provided a digital communications receiver comprising: an antenna for receiving a signal; a demodulator coupled to the antenna for demodulating the signal to obtain an information signal, the information signal having a dynamic range; a signal level adjustment circuit coupled to the demodulator for adjusting the signal level of the information signal; a control circuit coupled to the signal level adjustment circuit for controlling the same responsive to a parameter of the received signal; a digitizer for digitizing the reduced signal to obtain a digital signal, the digital signal having an amplitude; and a scaling circuit scaling the digital signal. A related method and computer readable media are also provided.
It is contemplated that the present invention may find application in a number devices including but not limited to cordless telephones, cellular telephones, whether CDMA, GSM, or TDMA, two-way radio systems, package or personal tracking devices, personal communications devices, wireless remote controls, baby monitors, and other wireless communications devices.